The present invention relates generally to a vehicle crash discrimination system for controlling deployment of a passenger safety restraint device, such as an air bag.
Conventional vehicle crash discrimination systems are primarily designed to protect vehicle occupants from frontal collisions. Frontal collision detection systems tend to employ sensors which use an inertial sensing mass to detect deceleration of the vehicle. Because of the distance between the vehicle occupants and frontal impact points on the vehicle, conventional inertial sensors provide satisfactory results when a deployment decision can be made at least 30-40 milliseconds after the initial impact.
However, conventional crash discrimination systems are simply inadequate when deployment decisions must be made within a few milliseconds, such as in side impacts. To accommodate this severely restricted decisional time period, known side impact detection systems rely on one of three sensor arrangements: a contact switch or crush sensor, a pressure transducer, or a modified silicon (inertial mass) accelerometer. Examples of such sensor arrangements can be found in U.S. Pat. No. 4,995,639 to Breed, U.S. Pat. No. 5,202,831 to Blackburn et al., U.S. Pat. No. 5,277,441 to Sinnhuber, and U.S. Pat. No. 5,231,253 to Breed et al.
While each one of these known sensor arrangements are more suitable than a modified conventional frontal crash discrimination system for side impact situations, each known arrangement suffers from inherent drawbacks. For example, contact switches only provide a one bit binary output (i.e., "on" or "off") which are typically based on the exceeding of a certain threshold of force. These thresholds must be carefully adjusted to allow the system to differentiate severe crashes from situations like door slams, opening of the door into a pole, etc. Pressure transducers only provide an output which is responsive to total force across the entire surface without being able to distinguish or isolate the force at different locations on the surface. Silicon accelerometers are only able to typically provide a very limited number of data samples within the allowed decision period, and therefore do not provide enough information to make reliable decisions. Furthermore, none of these known arrangements are suitable for reliably predicting the occurrence of a severe surface impact so that the safety restraint device can be actuated as early as possible.